The ubiquitin-dependent protein degradation pathway is essential for proteolysis of intracellular proteins and peptides. Enzymes that remove ubiquitin from ubiquitin-conjugated peptides like USP28 affect the fate and degradation of intracellular proteins and are essential for maintenance of cell-free ubiquitin pools (Valero et al. 2001).[supplied by OMIM Mar 2008]